Platoons are based on left hand hitting starters that have large platoon splits . Then you can generally find cheap RH hitters that can hit LH pitching but since they can't hit RH pitching they can't hold down a starting role anywhere and thus don't cost much. If you start with a RH hitter good enought to break into a starting line-up, it's generally because they either have a small platoon split to being with, or only have a platoon split because they hit LHP pitching at some all-star rate and still hit RHP better than the average average part time LHH that might be available.. Thus little platoon motivation. Platoon splits run higher for starting LHH batters across the league for this reason - a RHH batter with a big platoon split is simply less likely to ever become an everyday player.
The shift devalued LH hitting more than RHH so it's demise should re-establish the generally higher value of LH hitting starters and one result will be to increase the number of starters that benefit by being platooned so as to avoid facing LH pitching.